Natural ores containing antimony sulfides, or concentrates derived from such ores, are commonly roasted in air to recover the antimony values as the metal or oxide. This process generates large quantities of SO.sub.2 gas, an objectionable air pollutant. The roasting process also converts arsenic present in the ore to arsenic compounds incorporated as an impurity in the antimony product. This arsenic impurity may be tolerable when the ore or ore concentrate contains minute amounts of arsenic, but many ores contain such large amounts that the resultant product of air roasting is unacceptable.
These two aspects of air roasting -- generation of sulfur dioxide gas and failure to isolate antimony from arsenic impurity--are avoided by use of a wet process. One such wet process involves dissolving the antimony sulfides in an alkaline liquor and then oxidizing the liquor with oxygen or air. This normally very slow oxidation reaction converts the antimony to antimonate, which may be separated as an insoluble metal antimonate, while the products of oxidation of the sulfide ion remain dissolved in the liquor. Most of the arsenic remains in the ore residues as very insoluble compounds.